Osteochondritis Dissecans 

• Sub-articular, post-traumatic necrosis

• Occurs only on convex surfaces of bone

  • Medial condyle of femur

  • Capitellum

  • Proximal surface of talus

  • Head of 1^st metatarsal

• Most patients are athletic

• Direct blow is more common cause than a rotational injury

  • Knee lesions are more common amongst high jumpers

• Most common cause of an intra-articular loose body

Osteochondritis dissecans of medial femoral condyle-ovoid fragment
of bone is separated from surface of condyle but does not yet lie freely within the joint

• In adults, loose body contains larger fragment of cartilage than bone

• Possible outcomes

  • Death of bony, but not cartilaginous, portion of loose body

    • Loose body is invisible except to MRI

  • Complete resorption of loose body

  • Reincorporation or regrowth

    • Usually not in adults

    • In children, fragment is less likely to separate from bone and therefore more likely to reincorporate

• Cause of a “locking knee”